1. Field of the Invention
The present invention relates to pharmaceutical compositions. In particular, this invention relates to topically administrable ophthalmic compositions that contain certain combinations of two polymeric components.
2. Description of Related Art
The use of polymeric ingredients in topically administrable ophthalmic compositions is well known. Polymeric ingredients are typically used in suspension compositions as physical stability aids, helping to keep the insoluble ingredients suspended or easily redispersible. In solution compositions, polymeric ingredients are typically used to increase the composition's viscosity.
Many polymers have been used in topically administrable ophthalmic compositions. Included among these are cellulosic polymers, such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, and ethylhydroxyethyl cellulose. Also included are synthetic polymers, such as carboxyvinyl polymers and polyvinyl alcohol. Still others include polysaccharides such as xanthan gum, guar gum, and dextran.
Combinations of polymers have also been used in ophthalmic compositions. Certain combinations of polymers are known to provide synergistic effects on viscosity and, in some cases, even a phase transition from a liquid to a gel. For example, U.S. Pat. No. 4,136,173 discloses ophthalmic compositions containing a combination of xanthan gum and locust bean gum.
One approach to achieving a target viscosity in a topically administrable ophthalmic composition might involve simply adding a sufficient amount of one polymeric ingredient. Often, however, it is desirable to minimize the total amount of polymeric additives in topically administrable ophthalmic compositions. A mixed polymer system containing more than one polymer can significantly enhance the viscosity and lubrication property of a composition while minimizing total polymer concentration and cost of materials.